1. Field of the Invention
The present invention relates to a glass optical waveguide for use in light communication purpose, more particularly, the invention relates to an eccentric core optical waveguide.
2. Description of the Prior Art
An optical glass fiber of the known type consists of a central core portion having relatively high refractive index for passing light and a sorrounding cladding or jacket portion having relatively low refractive index. In the manufacture of such known glass fiber, an irregularity might occur, for instance, bubbles may be occluded between the core and the cladding. In such an occasion, deterioration of characteristics of the product, such as for causing a large scattering loss, is inavoidable. In order to overcome such difficulties, a construction, in which the core is supported in air, has been suggested. For instance, P. Kaiser, E. A. J. Marcatili, and S. E. Miller disclosed in Bell System Technical Journal (B.S.T.J.) Vol. 52, No. 2, February 1973 pp 265-269, a single material construction for holding central core by providing a supporting slab in a pipe. Both the core and the pipe are made from an identical material such as silica. This construction is called as single-material (SM) fiber.
Also Marcatili U.S. Pat. No. 3,712,705 disclosed an air clad optical fiber comprising core having polygonal cross section disposed within an outer protective circular jacket so that the core contacts the outer jacket solely along the vertices formed by adjacent pairs of sides. In the Marcatili U.S. Pat. No. 3,712,705, it is mentioned that the jacket of the optical fiber is more of a protective member and, hence, its optical properties are of less importance than are the optical properties of the cladding of a conventional optical fiber. In such a Marcatili airclad fiber guide comprising a polygonal core supported within a circular outer jacket, the light is basically transmitted concentratedly in the polygonal core by the geometrical effect. Due to such constructive principle of the known type optical fiber, the light may leak from the core to outside, when the optical fiber is bent. Furthermore, in the manufacture of such known optical fibers, a stringent requirement is imposed for the form and dimension of the parts.